Eren's vision was blocked by a dense amount of fog when he used the spatial tunnel to get to its other side.
The butcher couldn't even use his mana sense to navigate because the fog was interfering with his senses. So he used his soul sense and felt his surroundings.
He felt the void he was surrounded by. And the bone-chilling atmosphere that had no origins.
There was a faint glow everywhere around him. But it would be difficult to locate the light source. Eren knew what he was supposed to do. He just kept on walking in a random direction after Alephee told him that the space was magically enchanted to get him where he was supposed to go.